A photosensitive resin printing plate precursor including a photosensitive resin layer generally contains a soluble polymer, a photopolymerizable unsaturated bond-containing monomer, and a photopolymerization initiator as essential components in the photosensitive resin layer, and is optionally mixed with additives such as stabilizers and plasticizers.
There has been well known, as a method of forming a relief plate by forming projections and depressions on a surface of a photosensitive resin printing plate precursor, so-called “analog plate-making method” in which, using a photosensitive elastomer composition or a photosensitive resin composition, the composition is exposed to ultraviolet light through an original film to selectively cure portions of the composition which are to form an image, and uncured portions are removed with a developer (JP 11-65115 A, JP 2001-272776 A, JP 2014-142622 A).
There has been proposed, as a method of solving the problems such as manufacturing time and cost of an original film in the analog plate-making, a resin letterpress printing plate precursor comprising a photosensitive resin layer and a laser-sensitive mask layer element provided thereon, capable of forming an image mask in situ. The method of making such a resin letterpress printing plate precursor is a plate-making method in which laser radiation is performed based on image data controlled using a digital device to form an image mask in situ from a mask layer element, followed by exposure to ultraviolet light through the image mask and further development, similarly to the analog plate-making. That method is referred to as the “CTP plate-making method” in the field of resin letterpress printing plates. The CTP plate-making method reduces the above-mentioned problems of analog plate-making.
There is also known “laser engraving plate-making method” in which a relief of projections and depressions is formed by engraving with a laser (JP 2001-328365 A). That laser engraving is advantageous in that the shape of the relief can be freely controlled unlike relief formation using an original film. For example, portions to reproduce a reverse text on a material to be printed may be engraved deeply, and portions to reproduce fine half tone dots can be engraved into a shape with shoulders so that the half tone dot does not fall over under printing pressure.
High production efficiency has recently been required in a plate-making step and a printing step so that it has been required to perform time shortening of the plate-making step and to reduce time loss in the printing step, due to machine stoppage involved in crack occurrence during printing and replacement of a printing plate material, as much as possible.
There have been proposed, as the method of solving the above-mentioned problems, for example, a method of mixing a polyvinyl acetate derivative and a polyamide having basic nitrogen as disclosed in JP 11-65115 A and JP 2001-272776 A, and a method of reducing the degree of crystallinity of a partially saponified polyvinyl acetate and derivatives thereof as disclosed in JP 2014-142622 A.
The technique of JP 2014-142622 A exerted the effect of reducing crack occurred during storage of the plate material after printing, leading to time shortening of the plate-making step. However, under harsh conditions where the large number of sheets are printed with a pattern, which easily undergoes concentration of printing pressure because of particularly small relief area, without replacing a printing plate material as much as possible, crack still occurs sometimes in the relief during printing, leading to machine stoppage loss.
In view of the above-mentioned circumstances, it could be helpful to provide a photosensitive resin printing plate precursor having high water developability or rinsing properties for engraving residue, and image reproducibility, and that is also excellent in printing durability.